Antidiuretic response to piperoxan as a diagnostic test of pheochromocytoma.

† Observations on the renal functional effects of piperoxan in patients with hypertension due to functioning pheochromocytoma had shown that, in such patients, this drug provokes a decrease in urine flow. This suggested that, with standardized hydration, the effect of piperoxan on urine flow might be useful in the evaluation of patients suspected of these tumors. Accordingly, fasting, recumbent patients were given 1 liter of 0.25% solution of sodium chloride orally and urine was collected for three or four successive 30-minute periods, the usual test dose of piperoxan being given intravenously after the second urine collection, when its effect on blood pressure was also observed. In 3 normotensive patients and 32 patients with hypertension not due to pheochromocytoma, including 7 in whom piperoxan induced decreases of systolic pressure more than 30 mm. Hg, piperoxan had a diuretic effect, in that the volume of the third urine sample exceeded that of the second. The physiology of pheochromocytoma was then simulated in seven normal subjects by giving them infusions of levarterenol with and without a mixture of epinephrine. In these the diuretic response to piperoxan was not observed and antidiuresis occurred in those receiving the mixture of the two pressor amines. Further, in two patients with hypertension due to functioning pheochromocytoma, the volume of the third sample (after administration of piperoxan) was substantially less than that of the second urine sample. The procedure is described as a confirmatory observation in the diagnosis of functioning pheochromocytoma. It seems to have the advantage of giving normal, diuretic responses in patients who show non-specific depressor responses to piperoxan. Note is also made of the frequent occurrence of "false-positive" depressor responses to phentolamine in patients with essential hypertension under treatment with preparations of Rauwolfia.